1. Field of the Invention
The present invention relates to a method for determining an indicator for a blindness of a radar sensor, as well as to a radar sensor including a control and evaluation unit which is designed to carry out a method for determining an indicator for a blindness of the radar sensor.
2. Description of the Related Art
Published German patent application document DE 199 45 268 A1 describes a method and a device for the soiling and/or blindness detection of a sensor based on at least two indicators, which are formed from the signals received and/or transmitted by the sensor. The following indicators are provided: the mean angle quality of all objects detected by the system, the rate of detection failures of a target object selected for a vehicle longitudinal controller, a mean power of the signals received by the sensor, the total of all objects detected by the system during a measurement, the linkage of distance and amplitude of the detected object which is the farthest, as well as the road reflections detected by the system. For the determination of the mean power of the received signals, the power of all detected peaks in the spectrum of the received signals is added up and a mean value is formed.
Published international patent application document WO 2010/099988 A1 describes a radar sensor having a blindness detection device, a switchover between a measuring mode for the position finding of radar targets and a test mode being carried out. In the test mode, the control of the radar sensor is carried out on the basis of parameters which are optimized for the blindness detection device. If the radar sensor does not locate any preceding vehicles or objects of a similar size, a test for the detection of blindness may include the temporary increase in the range of the radar sensor. In additional examples it is examined whether the so-called “ground clutter” may be demonstrated or whether the so-called “rain clutter” is detected. In one example, the power is varied in the test mode between a higher value on a modulation ramp and a lower value on a different modulation ramp. In this way, states in which the sensitivity of the radar sensor is reduced are to be detected more sensitively and more reliably. A comparison between the signals, which are received in the test mode on the one hand at high power and on the other hand at a decreased power, is to make the sensitivity indicators more apparent and to make the blindness detection more robust against temperature and aging effects, which influence the behavior of the transceiver electronics.
A method for the detection of sensitivity losses of an FMCW radar locating device by diffuse sources of loss is known from published international patent application document WO 2010/097137 A1, in which the power of the transmission signal is varied cyclically, respectively after the completion of a modulation ramp, and a sensitivity loss is determined based on differences in the power features of signals which are received in successive modulation ramps with identical modulation. In one example, the total received transmission power for two identical modulation ramps having different power is integrated throughout a large subarea of the respective spectrum, and by subtracting a medium noise power, a signal power which is part of the peaks in the spectrum is determined. Their ratio to the noise power is calculated. In the case of a non-blinded sensor, these signal-noise-power ratios differ from zero for those two spectra and differ by a factor which corresponds to the ratio of the transmission signal powers divided by the ratio of the noise powers. In the case of blindness, both signal-noise power ratios are to become zero.